We are studying in the organizaffon and physiology of the liver. The liver is a very light-scattering sample and we have not been able to penetrate very far into specimens using standard confocal microscopy. We are limited to imaging only 20-30 micron in from the surface of the liver secffons. We will examine the ability of 2-photon microscopy to image fluorescent labeling at depths greater than 30 microns within liver cryosections. In addition we would like to test the feasibility of uncaging the photo-activatable fluorescent indicator (CL-NERF) using 3-photon excitation.. We will conjugate the indicator with a monoclonal antibody in order to localize the indicator to specific structures within liver tissue. This study was a feasibility study in order to obtain preliminary data to present in a shared equipment grant application for a commercial multiphoton system.